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Summary

Although estrogen was supposed to act mainly as a growth factor in promoting cancers, several lines of evidence now suggest that products produced by estrogen in the body may initiate cancer development by causing DNA mutations. Researchers have found, for example, that some estrogen metabolites can bind to DNA, triggering damage. These compounds also produce cancer in lab animals, while recent epidemiological work suggests that women who have reduced amounts of the enzymes that help sop up those reactive estrogen byproducts are at higher risk for developing breast cancer. But estrogen researchers are far from unanimous on which of estrogen's various byproducts is the culprit, and others question whether they play a role at all, because estrogens and their metabolites don't register as mutagenic in standard tests, and estrogen is present in the body in such small quantities that the effects of its metabolites should be negligible.